Basic Electrical Theory for the Everyman: Non-fiction Writing Contest Submission by elt2jv
Electricity is a mystery to the average person. Most of us know it involves the movement of electrons along a conductor and the analogy to flowing water. Beyond that, it gets fuzzy. In an everyday situation this is only a moderate inconvenience. For the DIY’er or in an emergency it can spell disaster. Having personally witnessed the results of sheer electrical stupidity, I write this article hoping to pass along some basic electrical theory and as much safety technique as I can describe.
First, there are two primary types of electrical circuits: direct current and alternating current. Direct current circuits are powered by a generator or a battery and develop a constant voltage. They are usually of a much lower voltage and can be found most commonly in automotive systems and portable electronics.
The current only flows one way though the circuit across the load. Alternating current circuits are powered by alternators, house current, or by a DC source via an inverter. In an AC circuit, the current flows both ways across the load. They are never interchangeable, ever. Hooking up an AC machine to a DC power source may damage both pieces of equipment, but is far less dangerous than hooking up a DC load to an AC source.
This is because DC sources are usually far smaller and less powerful than AC sources. I remember the result when a person I knew in the Navy hooked up a car stereo amp to the main current from a wall outlet in one of the dorms (he hadn’t been to his basic electricity class yet.) It took a few days to get a replacement transformer shipped in to restore power to that dorm. He’s lucky he wasn’t killed.
AC machines and their power sources are much more efficient than DC equipment, but AC cannot be directly stored in a battery. The losses in converting one form of current to another are greater in most cases than the difference in efficiency. This is why most systems that incorporate a battery are DC-only systems.
This is also a factor to consider if you are choosing a backup power system: if you are going to use battery power than you may be better off with DC equipment than with using an inverter for AC equipment. I’ve seen a lot of 12V equipment at truck stops and RV stores, and most of it is designed for traveling or space efficiency.
Voltage is the difference in electrical potential between two points on a circuit. The electrical potential in this case is the concentration of electrons. In a 12V system, this means that there are 12 volts of electrical potential difference between the positive and negative terminals of the battery. Voltage is analogous to the pressure of water in a pipe. Voltage is the potential to perform work against a load.
Current is expressed in Amperes (Amps) and is a measure of the amount of electricity passing a set point in the circuit. It is analogous to the diameter of a flowing water column in a pipe whose diameter is the limit of the conductor’s capacity. It affects the ability of voltage to perform work over time. Current is the limiting factor in the lethality of an electrical shock. At sufficient voltage, one tenth of an Amp is lethal.
Resistance is the measure of a component to impede the flow of electricity, usually by converting it to heat. This property is analogous to a constriction in a portion of the pipe. It is also responsible for heat generated by electrical equipment and fires from overload conditions.
Switches interrupt or divert current. Fuses and circuit breakers interrupt the current either by melting or opening a spring loaded switch to prevent overload in the rest of the circuit. Conductors are the metallic element that electricity flows along, usually wires.
Ground is also a conductor, specifically in automotive applications where the negative terminal connects directly to the vehicle frame and is used as a common conductor terminating most vehicle circuits. GFCI outlets are common in many homes and incorporate a fast-trip circuit breaker to protect from shock. For them to work properly, they must be grounded such that if a circuit shorts through a wet or broken device then the breaker will open and interrupt current.
All conductors have some resistance. Extension cords are no exception. Use of a long cord, or several in series, can result in decreased voltage available to do work at the terminal end. Connecting a device at lower than rated voltage can result in malfunction or failure to operate and is therefore unsafe.
The cords will also heat up with use and may cause a fire. The greater a load the cord must support, the shorter it should be and thicker (lower gauge number) the cord should be. Also, loads have a cumulative draw on a circuit. This differs between AC and DC circuits, but are essentially the same regarding current: add the current used (amps) of all the loads in the circuit and compare to that permitted across the fuse or breaker. Remain below that number of amps.
Never replace the fuse or breaker with that of a higher rating unless the circuit is designed for heavier loads. Most manufactured circuits have the fuse as the weakest link. A higher-rated fuse may shift that weak point off to another component, which may fail in an unwanted way.
When you work with circuits that may be live, such as when changing a fuse or resetting a breaker, only touch the component with one hand. This way if current shorts through you to the ground it will go through your arm and leg instead of across your chest where it might interrupt the normal electrical signals that control your heart.
I was taught to hold my belt at the small of my back with one hand while working with the other. In all cases, try never to have to work on live circuits. Getting shocked sucks. When connecting a device cord to an extension cord, connect the device first, and then plug it into the wall. This way if the device is shorted the current isn’t going across the two hands holding the two cords and thus across your chest. To prevent having the cords separate while in use and exposing the contacts, tie a half hitch or overhand knot with the two bitter ends of the cords before connecting them.
A short circuit is when the current is completed through an undesired path via a conductor. This can be a bare wire, water with enough electrolytes in it (most does) or even your body. An open circuit is when the circuit is interrupted, such as when a switch is open a fuse is blown or a wire is cut.
Devices are designed to run at their rated voltage, current and current type. Unless you know how to build the right kinds of circuits, do not operate anything above its rating.
Unless you know how to work with electronics, do not open up the covers on any electronic devices. There are components that store electricity similarly to batteries except that they can release all of their energy in an instant. They are called capacitors and they can light you up. The ones in old TV sets can blow you across the room. They can remain charged for years. You’ve been warned.
Polarity is the direction of current flow. Hooking up a circuit with reversed polarity is a sure disaster. Remember that in automotive circuits, black is negative and red is positive. The negative and positive terminals are usually of different sizes. If you find yourself forcing one terminal on and the other looks like it will be too loose, STOP. Letting the smoke out of all the onboard electronics (or at least the alternator) is not a good idea. When you jumpstart a car you have the opportunity to fry both, so watch what you’re doing.
Many tasks don’t really require electricity. We are, as a culture, unnecessarily dependant on convenient electric devices. If you’re in an emergency situation and your electric system is unsafe or needs repairs beyond your expertise then shut it off and leave it off unless you know how to fix it. There are too many things in electrical systems that you can only get wrong once.
I know I’ve left out a lot, but this ought to be a good primer and I hope it will inspire someone to learn more. Stay safe.